False-twist texturing yarn with torque jet

ABSTRACT

A process is disclosed for false-twist texturing yarn of synthetic thermoplastic polymer containing dispersed microscopic particles of an additive which is substantially insoluble in and unreactive with the polymer and is liquid at yarn temperatures used for heat-setting twist in the yarn. The examples illustrate improvements in twist-crimp obtained when the yarn contains 3.5 percent and 6.0 percent additive and false-twisting is accomplished at low tension with a torque jet.

United States Patent [191 Cochran 1 FALSE-TWIST TEXTURING YARN WITH TORQUE JET [75] lnventor: Stanley R. Cochran, Martinsville,

[73] Assignee: E. l. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Aug. 20, 1971 [21] Appl. No.: 173,426

[52] US. Cl 57/157 TS [51] Int. Cl D02g 1/02 [58] Field of Search 57/157, 164, 35, 57/140 R, 34 HS, 34 B, 157 TS, 157 F, 157

AS, 157 S [56] References Cited UNITED STATES PATENTS 3,009,309 11/1961 Breen et a1 57/34 B [451 July 24, 1973 3,388,104 6/1968 (rovnlt 57/157 AS Primary Examiner.lohn Petrakes Att0rney-Norris E. Ruckman [57] ABSTRACT A process is disclosed for false-twist texturing yarn of synthetic thermoplastic polymer containing dispersed microscopic particles of an additive which is substantially insoluble in and unreactive with the polymer and is liquid at yarn temperatures used for heat-setting twist in the yarn. The examples illustrate improvements in twist-crimp obtained when the yarn contains 3.5 percent and 6.0 percent additive and false-twisting is accomplished at low tension with a torque jet.

5 Claims, 1 Drawing Figure PATENTED 3, 747. 31 8 INVENTOR STANLEY R. COCHRAN BY V ATTORNEY FALSE-TWIST TEXTURING YARN WITH TORQUE JET BACKGROUND OF THE INVENTION This invention relates to a process for texturing yarn and more specifically, to a process wherein a traveling synthetic thermoplastic yarn is false-twisted about its own axis between forwarding means such that twist is accumulated upstream and is removed downstream of the point of twisting, and the upstream portion of the yarn is heat-plasticized to heat-set the yarn in its twisted configuration. The twist-crimped yarns produced are useful in the preparation of stretch fabrics.

Commercially available false-twisting devices are either false-twist spindles or friction tubes. Many varieties of false-twist spindle are well known, for example, those disclosed by Finlayson in U.S. Pat. No. 2,111,21 1, by Kunzle in U.S. Pat. No. 2,463,619, by Vandamme et al. in U.S. Pat. No. 2,761,272, and by Stoddard et al. in U.S. Pat. No. 2,803,108, to mention only a few. Friction-tube falsetwisters have more recently been described, for example, in Russell et al. U.S. Pat. No. 2,936,567, in British specification No. 928,877 to Spinner Osakeyhtio, and in Sabaton U.S. Pat. No. 3,527,043. Since all of these devices depend on yarn-friction for operation, they require substantial yarn-tension. Any modification of the process which reduces the amount of twist-crimping set in the yarn, or which requries speed-reduction for imparting the same amount of twist-crimping, is disadvantageous in this highly competitive industry.

. SUMMARY OF THE INVENTION The present invention is a false-twist texturing process which provides improved twist-crimping without speed-reduction, or which makes possible higher yarnspeeds without reduction in the amount of twist-crimp. The process also provides improved false-twist textured yarn.

In the process 'of this invention a heat-plasticized, drawn yarn of synthetic thermoplastic polymer containing about 2 to 7.5 percent by weight ofmolten additive, as finely dispersed discrete particles, is fed at uniform speed to a false-twisting torque jet of cool gas and withdrawn at a uniformspeed which provides a low tension of up to about 3 grams. The torque jet is arranged to form a vortex about an axis which coincides with the yarn path through the jet.

The additive is one which is substantially insoluble in, and unreactive with, the polymer. Its normal melting point should be less than l30C., and preferably less than about 100C. It should be finely dispersed throughout the polymer as discrete particles having individual volumes of less than about 100 cubic microns; preferably most of the particles have individual volumes within the range of0.2 to 50 cubic microns. Any additives meeting these requirements are satisfactory. Preferably an additive is selected which also improves the appearance or properties of the yarn, e.g., a delustering or antistatic agent. Methods conventionally used for dispersing such agents are suitable for forming the dispersions of additive in polymer for the present invention.

Unusually low tensions must be used in the present process. Much higher tensions have been needed in the commercial processes of the prior art for effective operation of mechanical false-twisters, and an additive of the above type will cause a reduction of twist-crimp in those processes. It is highly surprising, therefore, to find that twist-crimping is increased by the present invention. While various explanations may be offered for this unexpected result, the following may be involved:

Conventional processes use spindles or friction tubes for false-twisting at relatively high yarn tensions and applied twist is governed primarily by yarn-to-twister friction, generally increases with yarn tension, and is relatively independent of yarn modulus. The particular additives of the present invention cause a decrease in yarn modulus and, when processed with conventional false-twisting devices, some of the applied twist is pulled out by the high tension before the yarn cools sufficiently to resist loss of twist-crimp.

In the process of the present invention, however, available torque is independent of yarn-friction; and the effectiveness of twist insertion increases as yarntension is lowered down to a critical lower limit where buckling and pig-tailing of the yarn begin to occur. Low yarn tensions are readily obtained in the process of this invention. Moreover, the torsional rigidity of the yarn is reduced by the particulate additive both because of its negligible modules of elasticity'and because it reduces the effective cross-sectional area of each filament. Since in the process of the present invention available torque is independent of yarn friction, applied twist is now mainly governed by the torsional rigidity of the yarn as determined by yarn modulus and crosssectional area. Thus, even small changes in these key parameters diminish the resistance to torque twisting with the result that constant applied torque inserts more twist.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a diagrammatic representation of a preferred process in which yarn is drawn and forwarded directly to the false-twisting process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A yarn 10 containing uniformly dispersed particulate additive, as hereinafter more fully defined, is led from package 12 through guide-means 14 to the nip between driven feed-roll l6 and cott-roll l8. Draw-roll 20 (and cooperating separator-roll 22) forwards yarn 10 at a constant velocity higher than the constant feeding velocity of roll 16 whereby yarn 10 is drawn. Draw-pin 24, or other conventional device for localizing the draw-point, may be used. Spring-loaded roll 26, bearing against draw-roll 20, prevents backing of twist around the draw roll. Downstream, let-down roll 28 (and its cooperating separator-roll 30) withdraw yarn 10 at a constant velocity less than the drawing rate so as to maintain a yarn-tension between plasticizing-jet 32 and torque-jet 34 of up to about 3 grams. The twistcrimped yarn is wound up by conventional means, for example, ring-and-traveler wind-up 36.

False-twisting occurs in the linear yarn-path from the nip between rolls 20 and 26 to a point beyond the exit from torque-jet 34. Within plasticizing-jet 32, preheated gas is passed at high speed concurrently with yarn to cause plasticization. A symmetrical jet of the hot gas is formed so that its axis coincides with the yarn-path. Yarn I0 is highly twisted while passing through plasticizing-jet 32. Temperature and velocity of the hot gas are selected to overcome the yarns resistance to the twisted configuration. False-twist is inserted by torque-jet 34 win which a vortex of cool gas is formed so that its vortex-axis coincides with the yarnpath. The torque-jet causes twist to accumulate upstream of it and removes inserted twist downstream. Its cool gas is exceedingly efficient for deplasticizing the heat-set and twisted yarn 10. Since yarn makes, at most, only sporadic momentary contact with solid surfaces during both twisting and plasticizing, uniquely low yarn-tensions of less than 3 grams are readily obtainable. Apparatus suitable for use in practicing the above process is disclosed in Dugas application Ser. No. 28,583, filed Apr. 15, 1970, now U.S. Pat. No. 3,608,299.

While the drawing shows a preferred process of the present invention, various alternatives are also within its scope. Undrawn yarn may be fed to feed-roll 16 directly from yarn-spinning apparatus, or previously drawn yarn on package 12 may be fed directly to roll 20 without further drawing. Still further, yarn 10 on package 12 may be partially drawn so that drawing is completed between rolls l6 and 20.

Symmetrical hot-gas jets are preferred for plasticization (or heat-setting), but any conventional yarnheaters may be used. Tubular or slotted-plate heaters making little or no contact with the traveling yarn are preferred, but smooth low-friction hot plates are also effective if the yarn is maintained under low tension. Above 3 gm. tension, the efficiency of twist-insertion by known torque-jets decreases.

Yarns suitable for processing according to this invention are of any of the synthetic thermoplastic heatsettable polymers well known in the art. These include homopolymers and copolymers of polyhexamethylene adipamide, polycaprolactam, poly(methylene-di-1,4- cyclohexylene dodecanediamide), polyacrylonitrile, polyethylene terephthalate, and polytetramethylene terephthalate. Yarns most improved by the process of this invention are generally low-denier yarns used in knitting ladies sheer stretch hosiery, i.e., 10-20 denier monofilaments, 10-30 denier plural filament yarns, and 20-70 denier multifilament welt yarns.

Additives suitable for uniform dispersion throughout yarns to be processed are substances which are insoluble in and unreactive with the polymer and which are in liquid form at the maximum yarn-temperature during heat-setting. Ordinarily, the melting point should be below 130C., and is preferably below 100C. Less than 2 percent additive, by weight of the yarn, ordinarily provides insignificant improvement in twist-crimp; greater than 7.5 percent by weight additive causes spinning difficulties and reduced tensile properties result. If the dispersed particles are too large, non-uniformity of drawn-yarn properties results (including increased filament breaks). Each particle should have a volume of less than about 100 cubic microns, preferably from 0.2 to 50 cubic microns. In the fully drawn yarn, each particle is needle-like in shape, aligned with the axis of the yarn, has a diameter from about 0.1 to 0.5 microns, and a length of less than 1,000 diameters, preferably about 200 to 500 diameters. The particles are generally spherical in the polymer melt, and elongation increases throughout processing.

The additive should have essentially zero modulus with respect to the yarn at the temperature of plasticization so that it will contribute essentially nothing to the yarn s resistance to crimping. Additives which are molten at the plasticization temperature are found to meet this requirement. Preferred additives are waxy semi-solids or viscous liquids at room temperature.

Denier of a yarn is well understood to be the weight in grams of 9,000 meters of yarn tensioned only enough to straighten any crimp.

Modulus, as reported hereinafter, is the initial slope of the load-elongation curve (following straightening of any crimp) obtained at 60 percent/minute elongation on a continuously recording stress-strain analyzer. ltis reported as grams per denier (gpd), and is determined after equilibrating the yarn-package at percent relative humidity and 25C.

By applied twist is meant the amount of twist accumulated along a yarn during its plasticization. A springloaded device is used to take a sample of traveling yarn just upstream of the torque-jet. It does so by clamping both ends of about a 1.5 inch twisted length and simultaneously cutting the yarn just outisde both clamped points. The number of twists per inch (TPl) of this twisted and unrelieved sample is counted under a microscope.

Twist-crimp (CPI) is measured on the fully processed yarn. It measures process effectiveness. A length of monofilament, or a single filament removed from a multifilament yarn, is suspended from one end with a 1.2 mg./den. weight attached to the other end. Crimping is completed by exposing this specimen to atmospheric steam for 2 minutes. Without releasing the load, a portion of steamed sample is taped to a support and examined microscopically. The number of cyclical deformations per inch of crimped length is reported as CPI.

EXAMPLE 1 Three monofilament p olyhexamethylene adipamide yarns, nominally 15 denier when drawn, are prepared by the conventional melt-spinning process and packaged undrawn. Each batch of polyhexamethylene adipamide starting flake has a different level of finely dispersed polyethoxylated hydrogenated caster oil (HECO) having a 200:] mole ratio of ethylene oxide to castor oil. The three batches have additive at 0 percent, 3.5 percent and 6.0 percent, respectively, by weight of flake. Normal melting point of the HECO is about 60C., and it is a waxy solid at room temperature. Undrawn deniers of the monofilaments produced from the three polymer batches are 62.5, 59.0 and 59.0, respectively.

The false-twisting process shown in the drawing is used with two minor modifications. First, two monofilaments are led together through the process, being combined immediately after leaving packages 12. Secondly, the two processed monofilaments are separated downstream of let-down roll 28 and separately packaged. Draw roll 20 operates at constant peripheral velocity of 398 yd./min. Feed-roll 16 has a lower peripheral velocity such that yarn 10 is drawn to 4.106 times its original length. Let-down roll 28 has a constant peripheral velocity 16 percent less than that of draw-roll 20. Air fed to plasticizing jet 32 is preheated to 310C. and exits from the device at 195C. Torque-jet 34 has a 0.25 inch long yarn passage of 15 mils diameter, and roomtemperature air under psig. pressure is injected tangentially at the lengthwise midpoint to create the twisting vortex.

Each feed yarn is false-twisted on two separate apparatus assemblies, one inserting S-twist and the other Z- twist. Table I lists pertinent data and twist-crimp (CPI) results. The average improvement in twist-crimp with HECO present is about 9 percent, including the unexplainably low value for the S-twisted monofilament with 6% HECO.

A second larger scale test is performed at the same conditions as described above. Results shown in Table II are averages of many determinations not differentiating S- and Z-twist. It is seen that even higher improvements in twist-crimp result.

Microscopic examination of the drawn monofilaments shows the HECO to be particulate, elongated, and aligned with the filament-axis. Particle diameters are in the range 0.1 to 0.5 micron, averaging about 0.2 micron. Lengths are predominantly within 200 to 500 diameters. It is observed that the HECO-containing monofilaments are highly delustered, a desirable result Two 3-filament yarns of polyhexamethylene adipamide are prepared fromflake by conventional meltspinning. One batch of flake has no HECO; the other is 3.5 percent by weight HECO. The'process shown in the drawing is employed, the yarns being processed singly. Speed of draw-roll 20 is 500 yd./min. and feed-roll 16 is operated to draw the yarn to a 4.10X increase in length between rolls l6 and 20. Peripheral velocity of let-down roll 28 is 16 percent lower than that of drawroll 20. Air fed to plasticizing-jet 32 is preheated to 300C. Other conditions are as given in Example I.

The processed HECO-free yarn has a drawn denier of2l.1 and a CPI of 62.7. The yarn containing 3.5 percent by weight HECO has a drawn denier of 21.3 and a CPI of 67.2. The presence of HECO is seen to increase twist-crimp by an average of 7.2 percent.

I claim:

1. In a process for texturing yarn wherein drawn yarn of synthetic thermoplastic polymer is false-twisted between forwarding means such that twist is accumulated upstream and is removed downstream of the point of twisting, and the upstream portion of the yarn is heatplasticized to set the yarn in its twisted configuration; the improvement which comprises feeding heatplasticized yarn of polymer containing about 3.5 to 6.0 percent by weight of molten additive at uniform speed to a false-twisting torque jet of cool gas and withdrawing the yarn from the torque jet at a uniform speed which provides a low tension of up to about 3 grams; said torque jet being arranged to form a vortex about an axis which coincides with the yarn path through the jet, and said additive being one which is substantially insoluble in and unreactive with the polymer, has a melting point below 130C. and is finely dispersed throughout the polymer as discrete particles having individual volumes of less than about cubic microns.

2. A process as defined in claim 1 wherein the yarn is drawn and then forwarded to said torque jet for falsetwisting directly from the drawing operation.

3. A process as defined in claim 2 wherein said additive is a delustering agent.

4. A process as defined in claim 2 wherein said additive is polyethoxylated hydrogenated castor oil.

5. A process as defined in claiml wherein said polymer is polyhexamethylene adipamide. 

2. A process as defined in claim 1 wherein the yarn is drawn and then forwarded to said torque jet for false-twisting directly from the drawing operation.
 3. A process as defined in claim 2 wherein said additive is a delustering agent.
 4. A process as defined in claim 2 wherein said additive is polyethoxylated hydrogenated castor oil.
 5. A process as defined in claim 1 wherein said polymer is polyhexamethylene adipamide. 